Flexible electronics is becoming more and more important in the last years. In particular, flexible electronics can be important because it allows the integration of high performance electronic devices to several fields of application where typical electronics on rigid substrates could not be integrated. Flexible electronic devices can be easily integrated on several kinds of curved surfaces. For example, within the healthcare sector, electronic devices and circuits developed on flexible substrates can be exploited to monitor, for example, glucose blood level, temperature, pressure, etc. In such a way, electronic plasters, implantable sensors, etc., can be developed. The method and devices developed with the same may enable such sensors developed on a flexible substrate to be minimally invasive and more easily accepted by the patient since they are better adapted to the shape of the human body than typical electronic devices and systems. Other application fields include ambient intelligence, distributed sensors, electronics on textiles, energy harvesting, power management, and industrial electronics.
One potential issue relating to flexible electronics concerns the fabrication of flexible electronic devices. In particular, the fabrication of flexible electronic devices may be critical because it involves the handling of flexible, and thus fragile, semiconductor devices. Accordingly, the fabrication of flexible electronic devices is costly since it involves the employment of special handling and packaging tools suitable for handling flexible semiconductor devices without damaging them.
According to typical methods for the fabrication of flexible electronic devices, the silicon wafer is typically thinned down to less than 100 micrometers before preparing the single die. In particular, after thinning of the wafer, the die are prepared, for example, by way of solder bumping of the chip pads, and cut using several kinds of typical dicing methods, in order to further allow picking them out of the wafer substrate and placing on the final system, for example, a printed circuit board. However, the dicing of the thin system may be sensitive, and the single die may be damaged during this step. Moreover, the so prepared thin and flexible die may be manipulated using sophisticated pick and place tools and assembled on a flexible substrate. The fragility of the thin die and the sophisticated methods and tools used for carrying out these steps may render this process flow costly.
A further method for the fabrication of flexible electronic devices involves the Pick, Crack & Place® method, developed according to the Chipfilm™ technique to mount flexible die on a flexible substrate. In particular, according to this method, pre-processed wafer substrates having narrow cavities underneath the intended chip areas are fabricated. The cavities are formed at such a depth to obtain flexible die by fracturing the chip areas from the wafer at the level of the cavities. CMOS devices are formed in the chip areas, and trench etch is performed along the chip sides leaving anchors near the edges of the chips. Flexible die are thus obtained and processed by Pick, Crack & Place® in order to assemble the thin flexible dice on a flexible substrate. Also in this case, thin and flexible die are handled by the Pick, Crack & Place® method. The die may be easily damaged, and the method may be costly and difficult to carry out. Moreover, the realization of the electronic connections is also difficult because the thin and flexible die cannot be handled with high accuracy so that the positioning of the flexible dice at the correct connection positions is not readily realized.